2. Field of the Invention
The invention relates to systems and methods for communicating data among a plurality of devices interconnected on a bus. In particular, the invention relates to allocating system resources to accomplish efficient data communications.
2. Related Art
Conventional data communication systems such as that shown generally at 100 in FIG. 1, typically include a plurality of information processing devices 101-104 which communicate by exchanging messages over an information transfer medium or bus 105. Since only one communication can take place at a time, each device must compete for access to the bus when it has information to transmit to another device. Thus, when device 101 seeks to transmit a message to device 104, device 101 must first determine that bus 105 is not occupied by a data transmission between any other devices.
Numerous schemes have been used to arbitrate access to an information transfer medium, such as information transmission bus 105. For example, access to the bus can be granted by passing a token or by collision detection arbitration. In token arbitration, each device is allocated a time period during which it can access the information transmission medium. In those token passing systems which allow a device to hold the token until it transmits its complete message, devices holding a token for a long period of time can cause significant slowing of more urgent communications. In those systems in which a device may only hold a token for a limited period of time, it is possible that the device will not complete transmission of its message before it is required to release the token and bus access. Collision detection systems monitor information transfers on the bus by monitoring energy or voltage levels. When an energy level exceeds a threshold, the devices recognizes that two or more messages are on the bus at the same time. As a result, each information processing device 101-104 ceases transmission of its message and an arbitration scheme is executed to allow one device to access the bus first and another device to access the bus at a later time. A significant disadvantage of collision detection systems results from the time required to detect the collision and arbitrate access, thereby resulting in system latency.